In the welding operation, spatter removing has been a loss process. For the purpose of reducing spatters, a consumable electrode arc welding is conventionally well known (for example, see Patent Literature 1). In the method, a short circuit state and an arc generation state are alternately generated by changing the feeding direction of a welding wire periodically and repeatedly between the forward feeding and the reverse feeding.
FIG. 7 shows a time waveform of temporal change in a wire feeding rate and a welding output.
As a method for controlling arc welding where the short circuit state and the arc generation state are alternately generated in the wire feeding of a welding wire as a consumable electrode, for example, the following is known. According to the method, the structure contains a feeding rate controller and an output controller. The feeding rate controller effects control of a wire feeding motor in a manner that wire feeding is changed periodically and repeatedly between the forward feeding and the reverse feeding. The output controller controls welding output, as shown in FIG. 7. The controller decreases the output for a small amount of wire feeding and increases the output for a large amount of wire feeding. With the structure above, separation force caused by decrease in wire feeding rate in the short circuit state encourages the melted tip of the wire to transfer to the object to be welded. The structure decreases short circuit current that is a main cause of spattering, allowing a short circuiting transfer welding to continue with stability.
In the control method above (where the short circuit state and the arc generation state are alternately generated by changing the wire feeding periodically and repeatedly between the forward feeding and the reverse feeding), the description below discusses on a case where the object to be welded and the welding wire are mechanically released from the short circuit state by the reverse feeding. To attain the mechanical release, the wire needs to be fed in reverse at a feeding rate greater than the average feeding rate of wire feeding. To obtain the desirable feeding rate, a velocity amplitude has to be determined.
It is generally known that the wire feeding rate changes in proportion to change in welding current. In the control of a wire feeding rate with a periodical change, the average feeding rate of a wire feeding rate should be changed in synchronization with (in proportion to) the welding current. As the increase in welding current, the average feeding rate increases. Therefore, the velocity amplitude of the periodic wire feeding has to be increased in synchronization with (in proportion to) the average feeding rate. Besides, when the wire feeding motor can reach the load limit during the periodic wire feeding, the load on the wire feeding motor and the peripheral parts, such as gears, should be lightened by decreasing the frequency of the periodic wire feeding.
However, if the frequency and the velocity amplitude of wire feeding cannot be changed according to welding current, welding operation is limited at a fixed welding current, that is, the welding operation has to be carried out in a limited range of welding current.